According to a new analysis of longitudinal data by Penn State sociologist Paul Amato, whose work on divorce and relationship education programs we often cite in this space, cohabitation and marriage provide similar boosts to the mental health of young men and women. For women, however, the benefits are only temporary.

Amato used three waves of data from the large National Survey of Adolescent to Adult Health to investigate changes in the mental health of young adults as they got married or entered cohabiting relationships. To address the issue of selection—in this case, the likelihood that married people's health advantages are at least partly driven by healthier people's greater likelihood of marrying—he utilized a fixed effects model with "controls for age (and age squared to account for non-linearity), years of education, hours of employment and whether respondents have biological children." Survey respondents had a mean age of 16 in the first wave of data and 29 in the final wave, so most were single at the beginning of the survey and many were cohabiting or married by the end (only those with mental health data predating a cohabiting/marital relationship were included).

Men and women showed equal declines in depression symptoms and similar declines in suicidal ideation upon entering marriage. The effects of cohabitation on mental health were very close to those of marriage (slight differences showed up, but for both measures, they were statistically insignificant). Over time, though, the positive effects of cohabitation/marriage on mental health faded for women, while the advantage of partnered men over their single peers persisted through the duration of the survey.

Amato proposes that the gender difference arises because "women are more attuned to relationship quality than are men":

That is, women tend to monitor and think about relationships more than men do, and they tend to become aware of relationship problems more quickly. In fact, research consistently shows that women are less satisfied than men with their marriages and romantic relationships. Consequently, it is probable that the decline in mental health following the transition to marriage (or cohabitation) reflects women's growing awareness of and sensitivity to relationship problems.

Gender differences in the effects of marriage—differences generally favoring men—have shown up in previous research as well. The gap is part of a surprising paradox that Scott Stanley has touched on before. Despite benefiting more from marriage than women in certain respects, men are more reluctant to tie the knot, at least according to popular stereotypes, and young men are less committed than young women to their current partners (whether married or cohabiting).

Amato's discovery that cohabitation and marriage had almost identical effects on mental health stands in contrast to some previous studies concluding that marriage was more beneficial. He believes the findings "suggest that it is the social support provided by marriage, rather than the institutional nature of marriage, that is beneficial for emotional wellbeing. After all, one doesn't need to be legally married to a residential partner to enjoy companionship, intimacy and everyday assistance. Moreover, living together and marriage provide the same economies of scale, which can reduce people's feelings of economic stress."

As he goes on to point out, however, cohabiting relationships are more likely to break down, so one can't conclude from his findings that marriage and cohabitation are interchangeable.